In April, Iran began charging ships transiting the Strait of Hormuz a “toll” for safe passage. By itself, this represents a dangerous new dynamic in the Middle East that may have begun with the Houthis in Yemen as early as 2024, wherein parties extort international commerce by imposing fees in exchange for safe transit as part of their war effort. Although some countries have agreed to pay Iran’s fees, many countries such as the United Kingdom as well as organizations, including one representing the majority of tanker firms, have condemned it.
Iran’s latest proposal to control and charge ships for safe passage in the Strait of Hormuz as part of its ceasefire negotiations with the United States is far more dangerous, with global implications. If the United States were to recognize or endorse Iran’s (or any other state including Oman’s) control over navigation in the Strait, it would further exacerbate these risks. Such agreements might set a precedent that would support the strategic claims of U.S. adversaries and potentially destabilize international trade. The United States is pushing back with Operation Project Freedom but Iran seems equally determined to alter the status quo in the region.
The Strait of Hormuz and International Law
The Strait of Hormuz qualifies as an international strait under the United Nations Convention on the Law of the Sea (UNCLOS). It connects exclusive economic zones (EEZs) in the Persian Gulf with EEZs in the Gulf of Oman—and is used extensively for international navigation. It therefore falls within Article 37 of the Convention and is, in principle, subject to the Convention’s special regime applicable to straits used for international navigation.
Under that regime, navigation is governed by the rules of transit passage, which guarantee continuous and expeditious navigation and overflight to ships, aircraft, and submarines. Transit passage cannot be suspended. The legal regime’s objective is to strengthen the protection of navigation and reduce coastal state discretion. The latter retain limited powers, including with respect to safety and pollution. However, these powers are narrowly framed and cannot “discriminate in form or in fact among foreign ships or in their application have the practical effect of denying, hampering or impairing the right of transit passage.” This regime is designed to prevent coastal states from turning geographic chokepoints into instruments of control.
The difficulty is that Iran and other states contest the applicability of the transit regime to the Strait of Hormuz. Iran signed but did not ratify UNCLOS. Under the Vienna Convention on the Law of Treaties, signature alone is not sufficient to bind Iran to the rules of transit passage. In fact, Iran has rejected the blanket application of transit passage, particularly to non-UNCLOS parties. In Corfu Channel, the International Court of Justice (ICJ) famously recognized a right of innocent passage through straits used for international navigation in time of peace and invalidated Albania’s attempt to require authorization from the United Kingdom prior to using the channel. Transit passage is more robust than innocent passage and constitutes one of the Convention’s main legal innovations: “Whereas innocent passage as an exception departs from the sovereign rights of the coastal State in its territorial sea, transit passage as a rule entails a right for the flag State subject only to some limited and well-defined obligations vis-à-vis the coastal State.” Importantly, the right of transit passage does not afford the coastal state the right to prevent passage which is not innocent.
Oman, another coastal state whose neutral status in the Iran conflict is questionable, is a party to UNCLOS but entered a declaration emphasizing its authority to take “appropriate measures” to protect its security interests in the context of navigation in international straits. The United States is also not a party to UNCLOS but recognizes transit passage as part of customary law. At the same time, neutral states that are party to UNCLOS have the right of transit passage in the Strait of Hormuz by virtue of the Convention. The result is that the key actors—Iran, the United States, Israel, and Oman, among others—are subject to partly overlapping and partly divergent legal obligations when it comes to navigation in the Strait.
This raises the question as to whether transit passage has become customary international law, in which case it would apply even to states that are not party to UNCLOS. Mark Nevitt, Pnina Sharvit-Baruch, and others have argued that the right of transit passage has crystallized into custom, pointing to the widespread acceptance of UNCLOS and consistent practice by user states. Others take a more cautious view. As one recent commentary adequately suggests, transit passage may not have fully attained customary status—and even if it has, Iran would not be bound by the emerging norm as it has persistently objected to it.
In our view, the absence of a consensus does not open the door to unilateral or joint control by coastal states. On the contrary, it reinforces the need to identify a baseline by which all actors are bound—namely, a customary right to nonsuspendable innocent passage. Regardless of the view one takes on the Strait’s legal status, proposals allowing Iran and Oman (or any other state) to monitor navigation or issue permits and transit fees would be difficult to reconcile with international law.
First, such proposals are inconsistent with the more restrictive and treaty-based regime of transit passage. Under UNCLOS, transit passage is not subject to discretionary authorization by coastal states. They may regulate passage, but they may not condition passage on prior permission, impose general fees, or selectively grant access. An arrangement like Iran’s proposal that institutionalizes such control—even if framed as facilitative or cooperative—would run directly counter to the Convention’s purpose and would be incompatible with the rights of UNCLOS’s 172 state parties.
Second, even if one adopts a more cautious and realistic view and treats transit passage as non-customary, the proposed arrangements would still violate the baseline reflected in Corfu Channel and the customary, nonsuspendable right of innocent passage. The ICJ made clear that passage through international straits cannot be made dependent on the discretion of the coastal state during peacetime. A regime that conditions navigation on political alignment, authorization, or payment would exceed what even a restrictive reading of customary law permits. Claims that coastal states may “close” or operationally control the Strait of Hormuz tend to conflate the limited regulatory powers afforded by international law to coastal states with a broader authority that international law does not recognize. Granting discretion to Oman and Iran over the implementation of the right of innocent passage would contradict customary international law.
Third, the proposed arrangements cannot be justified under the law of naval warfare in situations of armed conflict. Assuming, for the sake of argument, that UNCLOS and the Corfu Channel test are displaced by the rules of naval warfare as lex specialis, given the ongoing conflict between Iran, the United States, and Israel, the proposed agreement would fall outside the recognized framework of lawful belligerent action at sea. The existence of hostilities does not grant coastal states a general right to control navigation in international straits. Belligerent rights at sea are exceptional and tightly regulated. Measures such as visit and search, capture, or blockade are permitted only under specific conditions and subject to constraints of necessity, precautions, and proportionality, as reflected in the San Remo Manual on International Law Applicable to Armed Conflicts at Sea.
A standing arrangement whereby coastal states would condition passage through the Strait of Hormuz on authorization, fees, or political alignment does not fit within this framework. It is not a lawful blockade, which must be formally declared, effectively maintained, and applied impartially, according to the San Remo Manual. Nor is it a case-by-case exercise of belligerent rights. A bilateral arrangement that purports to regulate access to the Strait in times of conflict would amount to a permanent system of administration and control and falls outside well-established norms governing naval warfare.
Conclusion
Any proposal to grant Iran, Oman, or any other state control over access to the Strait of Hormuz is likely incompatible with international law. This conclusion does not depend on resolving the debate over whether transit passage has attained customary status. Even in the most cautious view, grounded in the customary right of nonsuspendable innocent passage, neither the law of naval warfare nor international law permits coastal states to condition navigation through an international strait on authorization or payment in either peace or armed conflict.
As the United Nations Security Council affirmed in March, any “attempt to impede lawful transit passage or freedom of navigation in these international waterways constitutes a serious threat to international peace and security.” A regime that subjects passage to the discretion of coastal states would contradict that logic and have profound legal and geopolitical effects far beyond the immediate Gulf region.
An agreement granting Iran and Oman authority to allocate access, impose fees, or otherwise condition passage would risk setting a precedent that others may invoke. Russia, for example, has claimed that the Northern Sea Route between the Atlantic and Pacific Oceans constitutes territorial waters, which it has the right to control. The United States disputes this by relying on the same principles that would prevent Iran and Oman from exercising state control or tolling the Strait of Hormuz.
Similarly, a regime change in the Strait of Hormuz could substantially influence maritime disputes in the Pacific. China has often asserted that the Taiwan Strait and parts of the South China Sea are internal waters and can therefore restrict others from transiting them. The United States actively disputes this, including by conducting freedom of navigation operations, based in part on the arguments that keep states from exercising control over the Strait of Hormuz. Any U.S.-endorsed change in the status of the Strait of Hormuz could strengthen China’s argument and prompt other countries to assert similar claims. The stability of the transit regime depends on restraint by coastal states in many geopolitically-strategic locations around the world, including in Indonesia, Egypt, and Yemen.
In other words, the United States endorsing any plan that recognizes Iran’s or another country’s attempts to charge ships, grant permits, selectively authorize passage, or impose traffic restrictions on the Strait of Hormuz—thereby changing the status of the Strait—would pose geopolitical risks. It could not only escalate tensions in the Pacific, but also potentially spread to other global maritime chokepoints and impede the stability of maritime commerce and the freedom of navigation.
